You can read about science all you like, but until you see it in live action you never grasp the little moments that fill you with wonder. Here is such a moment for me…
This past semester my professor showed us the following video of a neutrophil (a kind of white blood cell) chasing after a Staphylococcus aureus bacterium. Keep in mind that there is no “intelligence” going on here, the cells can only move in response to millions of independent environmental stimuli:
For those of you interested, here’s what’s happening:
First of all, the class I was taking was graduate cellular structure and function, which overviews all of the major components of the cell and how they generally function. The day my instructor showed us the video we were reviewing the cytoskeleton, literally “the skeleton of the cell.”
Each time the neutrophil (the bigger cell) moves, it physically stretches its membrane out in the direction it wants to go while pulling on its membrane at the opposite end, accomplished by growing and shrinking various parts of its cytoskeleton. This video is fantastic because you can actually see the membrane push forward before the contents of the cell (organelles, storage vacuoles, and phagosomes) slosh forward to fill in the new space.
The bacterial cell moves a little differently. S. aureus has a fairly rigid cell wall, so expanding out parts of its membrane like little “false feet” (pseudopodia) is not a viable way to move. Instead, it likely uses flagella, long whip-like tails. While it’s hard to direct a cell in a specific direction with flagella (which only spin in one of two directions), they are quite effective at going “anywhere but here” as you can see in the video.
Regardless of the method by which the cells move, they both respond to environmental signals. In their outer membranes, each cell has numerous receptors that are constantly “tasting” the environment for “good” (attractors) and “bad” (repellers) particles. When the bacteria “tastes” the macrophage’s normal secretions or touches it physically, it responds by swimming away. These signalling systems may seem primitive, but they make such a chase as you see above possible on a micro level.
If you can’t tell, cell motility is what I’m currently studying in the laboratory. Feel free to check out my blog or my Twitter feed, links are in my signature above!